In recent years, plant-derived resins have attracted attention as an alternative for petroleum-derived resins, and active investigations have been made on the practical use of resin compositions using a variety of plant-derived resins. For examples of the use of the plant-derived resins, aliphatic polyester resins are particularly watched and are a commercial reality for various applications.
The aliphatic polyester resins are mainly used for the applications, such as containers and packaging, films for agriculture, and the like, based on using for a short period and disposing after used. However, the using span of such resin has been recently expanded to use in durable goods that require initial properties to be maintained for a long period, such as casings for home electrical appliances or OA apparatuses, and automotive parts. In recent years, as a plant-derived aliphatic polyester resin under particularly active research and development, there are known polylactic acid, polybutylene succinate, polyglycolic acid, polyhydroxyalkanoic acid, and the like.
However, an aliphatic polyester resin is easily hydrolyzed in comparison with a conventional general-purpose resin, and thus it has poor durability. Therefore, in order to maintain the initial properties for a long period, it is necessary to improve hydrolysis resistance of an aliphatic polyester resin.
In order to improve hydrolysis resistance of an aliphatic polyester resin, a compound having a functional group that is possible to block carboxy group terminals of the aliphatic polyester resin such as a carbodiimide compound and an epoxy compound is added.
A carbodiimide compound is a compound having a carbodiimide group represented by “—N═C═N—” in the molecule, and basically produced by well-known methods (see, for example, Patent Document 1, Non-Patent Document 1 and Non-Patent Document 2).
Addition of 1% by mass of polycarbodiimide compound excellent in heat resistance and stability to an aliphatic polyester resin is also proposed (see, for example, Patent Document 2). In this aliphatic polyester resin composition, a carbodiimide group reacts with and blocks free carboxy group terminal of the aliphatic polyester resin, thereby improving hydrolysis resistance of the aliphatic polyester resin.
However, when an aliphatic polyester resin is used in durable goods, it is necessary to increase the addition of polycarbodiimide compound to 5 to 10% by mass for obtaining sufficient hydrolysis resistance. Although the addition is increased, it is impossible to achieve a certain level or higher level (about 200 hours during which 70% of average molecular weight is maintained at 80° C. and 95% RH) of hydrolysis resistance. Thus, there has been a demand for further improvement in hydrolysis resistance.    Patent Document 1: Japanese Patent Publication No. 47-33279    Patent Document 2: Japanese Patent-Laid Open Publication No. 11-80522    Non-Patent Document 1: J. Org. Chem. 28, 2069-2075 (1963)    Non-Patent Document 2: Chemical Review, 81, 4, 619-621 (1981)